As mankind continues to develop around the world, the demand for energy rises. Most energy used to power machines and generate electricity is derived from fossil fuels, such as coal, natural gas or oil. These supplies are limited and their combustion causes atmospheric pollution and the production of carbon dioxide, which is suspected to accelerate the greenhouse effect and lead to global climate change. Some alternative approaches to produce energy include the harnessing of nuclear energy, wind, moving water (hydropower), geothermal energy or solar energy. Each of these alternative approaches has drawbacks. Nuclear power requires large capital investments and safety and waste disposal are concerns. Wind power is effective, but wind turbines require a windy site, often far away from grid connections and take up large footprints of land. This energy production system also requires continual mechanical maintenance, and can have an impact on the aesthetics of the surroundings and wildlife. Hydropower requires the construction of large, potentially environmentally harmful dams and the displacement of large volumes of flowing water. The number of such flowing water bodies is highly limited, both regionally and in an absolute sense. Geothermal power requires a source of energy that is relatively near the surface—a characteristic not common to a large portion of the Earth—and has the potential to disrupt the balance of forces that exist inside the Earth's crust. However, solar is one of the cleanest and most available forms of renewable energy and it can be harnessed by direct conversion into electricity (solar photovoltaic) or by heating a working fluid (solar thermal).
Solar photovoltaic (PV) technology relies on the direct conversion of solar power into electricity through the photoelectric effect in a solar cell: solar radiation impinging on semiconductor junctions can excite pairs of conduction electrons and valence holes. These charged particles travel through the junction and can be collected at electrically conductive electrodes to form an electric current in an external circuit. A PV module can include at least one solar cell that can be a part of a solar laminate, and can include a supporting frame. A solar laminate can have at least one solar cell between two layers of encapsulant. A PV module can also have a supportive backing under the solar laminate and connected to the frame to provide additional support for the solar laminate.
Photovoltaic is one of the most promising technologies for producing electricity from renewable resources, for a number of reasons: (1) The photovoltaic effect in Si and other solid-state semiconductors is well understood and the technology fully validated; (2) PV power modules convert solar power directly into electrical power, have no moving parts and require low maintenance, and can be located on almost any surface due to relatively light weight and thin profile; (3) Solar radiation is quite predictable and is at a maximum during hours of peak electricity consumptions; and (4) The industry has been aggressively pursuing a performance improvement and cost reduction path, approaching market competitiveness with traditional energy resources in many parts of the world.
There are two measures of value to the customer that is utilized in the industry. The first is the installation cost of the system. The metric that is most widely used for comparison is the total system cost divided by the name plate power of the system in Watts. The unit for this metric is $/W. The second measure is the cost of energy delivered over the lifetime of the system. This is referred to as the Levelized Cost of Energy or LCOE. LCOE in dollars per kilowatt-hour ($/kWh) is calculated by dividing the system cost and maintenance costs by the energy produced by the system during its expected life. Customers decide whether or not to convert to solar energy based on LCOE and decide which vendor to use based in $/W. It is thus desirable to reduce both metrics.
As the price of photovoltaic (PV) modules continues to fall, the cost of ownership (both in terms of $/W and $/kWhr) of a PV system is increasingly being dictated by the so-called balance of system costs. For a rooftop installed PV system, these include the following specific items:
1. Power management hardware: These include parts such as inverters, optimizers and rapid shutdown electronics.
2. System installation hardware: All the racking, mounting, roof attachment, skirting, nuts and bolts, and other pieces of hardware that are required to secure the PV modules to a roof.
3. Labor costs: These include the labor to install the system installation hardware, attach the PV modules to the hardware, the electrical wiring of the PV modules to each other and to the power management hardware, the integration of proper grounding to all exposed metal and the upgrading of the roof if required.
4. Permitting: The act of receiving a permit from the town to operate the PV system. This requires adherence to local and national codes, including fire and electrical codes. Furthermore these systems might need sign-off from professional engineers, fire marshals and other professionals.
5. Supply chain logistics: The cost of keeping inventory of multiple parts, issuing, storing and carrying all these parts onto the roof. Ensuring that parts and personnel expertise match at the site etc.
6. Indirect Costs: Operating equipment such as vehicles, ladders, lifts and tools. Administrative costs such as payroll, insurance, warranty servicing, and management.
7. Cost of sales: This includes marketing and sales; the time and effort required to identify and obtain the customer. The cost of sale is often independent of the size of the system.
The first two items (1 and 2) on the list above are direct material costs to the system, while items 3 and 4 are direct costs, and items 5, 6 and 7 are considered overhead. This means that items 1 through 4 typically scale with the size of the system where items 5 and 6 are independent of the size of the system.
From the above it will be clear that it is desirable to minimize both the direct labor and material cost of any system in order to reduce the overall cost of the system and therefore increase the probability of selling and installing a system. In addition, minimizing the costs of each installed system will directly reduce the overhead costs attributable to each system. Furthermore, increasing the size of the installed system will proportionally reduce the indirect cost of the system.
Rooftop PV systems can be installed using a variety of existing mounting hardware. Existing mounting solutions can generally be categorized as “railed” or “rail-less”. As the descriptive name indicates, the former includes long beams, or “rails”, typically made of aluminum metal, that provide support to the array of modules. The rails are especially required in regions where the solar modules can be exposed to heavy snow loading because the module construction is not adequate to support the additional weight of the snow. The rail-less systems offered commercially by companies such as Pegasus Solar and Zepp have gained market traction because of the ease with which they can be installed. This reduces the installation time and therefore direct labor of the system. However, these systems cannot be used in regions of heavy snow or wind loading because they do not provide the additional structural support necessary to meet local codes and requirements. Both the railed and rail-less systems are attached to the roof using a large number (typically 30-50) of individual metal parts, including bolts, nuts washers, multi-part clamps and brackets, as described in U.S. Pat. No. 9,800,199, titled ROOF ATTACHMENT ASSEMBLY FOR SOLAR PANELS AND INSTALLATION METHOD, U.S. Pat. No. 9,496,820, titled PHOTOVOLTAIC MOUNTING SYSTEM AND DEVICES, U.S. Pat. No. 9,473,066, titled MOUNTING ASSEMBLIES FOR SOLAR PANEL SYSTEMS AND METHODS FOR USING THE SAME, and U.S. patent application Ser. No. 14/054,807, the entire disclosures of which are incorporated herein as background information.
Although rail-less systems can be installed more quickly, current art unfortunately only teaches rail-less systems that cannot withstand all required snow and wind loads experienced around the world. Current options to increase load capabilities is to either increase the thickness of the module glass, or increase the stiffness of the mounting frame or utilize a framed system that mounts the PV module in such a way that high snow load conditions do not cause failure in the PV module components. These solutions come with the burden of added weight, size and installation time as will be known to those skilled in the art.
The use of metallic parts, in combination with the aluminum exterior frame that is part of a standard PV module construction leads to the requirement to electrically ground the rooftop PV system. Grounding often requires heavy copper cable that must be connected to a copper rod driven into the ground at the foundation of the building. Grounding is usually required to be done by a licensed electrician, further increasing both hardware and labor costs.
Overhead and indirect cost are not dependent on system size and contribute a significant portion of the total cost of the system. Cost-of-sales, or the cost of identifying and acquiring the customer, can be the single largest overhead item in a smaller, residential installation. Therefore it will be desirable not only to reduce the indirect costs by making the system easier to sell for instance, but it is also desirable to sell and install the largest possible system per costumer. Additionally it is desirable to make the installation process as efficient as possible. For example, doubling the speed of installation would allow the same installation crew to generate about twice as much revenue, reducing the fixed overhead cost allocated to each system by 50%, providing significant operating leverage for the installer.
A PV module can include a solar laminate that includes at least one solar cell, a supporting backing under the solar laminate, and a supporting frame around the perimeter of the PV module. The majority of solar PV modules utilize an electrically conductive aluminum frame that surrounds the entire module. This frame serves as a structural enforcement that assists the glass front face of the module to protect the fragile solar cells from the environment, including structural loads from wind and snow accumulation. The frame also serves as the interface between the module and the mounting system that secures it to a roof or the ground in an existing PV installation system.
Mounting systems that are structurally attached to the roof are typically made from conductive metal. The mounting systems typically consist of a multitude of parts that allow the installer of the system to connect the system to the rafters of the house or to a metal roof covering, provide structural stability, secure the module to the roof and provide the ability to adjust the installation so that it aesthetically aligns with features of the roof.
As can be appreciated by those skilled in the art, there are a number of deficiencies with current PV module mounting systems. These can be summarized as follows:
1. Exposed metal on the modules require the modules as well as the mounting system to be grounded. This requirement has the drawback that a means of electrical conductivity must be established between the module frame and the earth ground. This increases the amount of material and labor required for a PV installation and thus the cost. Furthermore, the new NEC 2017 electrical code requires that all grounded PV systems have a means of rapid shutdown that disconnects the modules from each other electrically. These rapid shutdown systems are costly and take time to install, further driving up direct costs to the PV system. In addition, the voltages in modules are increasing to reduce power loss in the conducting wires. Having cells at high voltage while the frame is at ground is the driving force for Potential Induced Degradation (PID), a major contributor to the gradual loss in power generation capacity of a PV module
2. Mounting systems require a significant amount of assembly on the roof.
3. Mounting systems require precision layout, measuring and attachment to the roof.
4. Rail—less systems reduce the amount of assembly steps and thus decrease the time of installations. However, when utilized in conjunction with standard modules, they cannot withstand high snow and wind load conditions.
5. The large number of parts of mounting systems require significant resources to maintain inventory, schedule deliveries and issue parts to crews going to the job-site. This logistic burden increases the indirect costs of systems.
6. Inability to release the module from the roof without proper tools increases the time to repair units and can obstruct firefighters from performing their duties.